1. Field of the Invention
The present invention relates generally to a fuel tank for receiving and maintaining fuel for a vehicle and in particular to a fuel tank which holds and dispenses both a liquid and a gaseous fuel.
2. Description of the Related Art
Modern transportation requires the extensive use of over-the-road vehicles such as automobiles, vans, trucks, and the like. Presently, such vehicles are powered by an engine which is fueled by gasoline or diesel fuel. The use of such fuels has given rise to two apparent shortcomings. First, such fuels are in limited supply throughout the world and the international control of such fuels causes their price and availability to be uncertain. A second shortcoming of such fuels is their adverse impact on the environment. It is well known that the hydrocarbon gases released from the combustion of gasoline or diesel fuel in an internal combustion engine are environmentally undesirable.
Natural gas exists in the United States in bountiful supply and the combustion of natural gas is environmentally compatible. Internal combustion engines can operate efficiently on natural gas. However, the use of natural gas as a vehicle fuel has been constrained by the "range" afforded the vehicle using such fuel. In the past, tanks of compressed natural gas have been placed in the trunk or other passenger/cargo carrying areas of the vehicle and interconnected with the fuel system for passage to fuel injectors or the like. However, the availability of storage areas in vehicles suitable for receiving such tanks of compressed natural gas is somewhat limited and such limitation necessarily constrains the distance that the vehicle can travel without refueling. Accordingly, the range of vehicles employing natural gas fuel has necessarily been significantly limited in the past.
The prior art is substantially devoid of the presentation of a vehicle having an internal combustion engine with fuel tanks provided as a structural portion of the vehicle to serve for holding both liquid and natural gas fuel for use by the engine. The requirement that the natural gas be introduced into the fuel tanks at high levels of pressure have typically dictated that the tanks be specially designed for simple retention in storage areas of the vehicle, and the prior art has not envisioned a manner for incorporating dual fuel tanks holding both gasoline and natural gas or any other liquid or gaseous fuel. The prior art has envisioned the use of natural gas as the fuel for vehicles as being more of a novelty feature for use by vehicle fleets serving a limited area, rather than an alternate fuel to the use of gasoline and diesel fuels which may be selectively used by the operator from a dual-fuel fired tank.